I’m lying on the floor of my apartment on a bloody towel. Hovering above me are the first man I ever slept with and the man with whom I currently sleep: my husband. One of them is cutting into my flesh, and yet I am calm, still and unflinching.

Although it sounds like a nightmare, this really happened. Let me explain.

I’m one of those women who stay in touch with a number of old boyfriends. People fall into one of two camps about this, finding it either utterly unthinkable or just plain common sense: If a lover was in your life because he was, well, lovely, then keeping him around is a benefit of a good ending. No doubt it takes a special kind of husband to be comfortable with this. I happen to have one of those.

When Bob and I moved to San Francisco early in our marriage, we reconnected with my old boyfriend Mark, who was in his orthopedic residency there. My husband immediately cottoned to Mark’s affable nature, his zest for adventure and the outdoors. We often double-dated.

In college, Mark had a headful of curly hair and a wicked sense of humor. Layer on intellect and empathy, and you had one hell of a catch. But I was eager to start life unencumbered by a relationship. We were “sliding doors”—potentially right guy but at the wrong time, so the doors never quite lined up.

Soon after we buddied up again in San Francisco, a weird bump appeared on my inner thigh, and it felt natural to hoist up my shorts and ask Mark to examine it. Why bother going to a doctor if your friend makes house calls?

“Looks like a simple cyst,” he said. “Nothing to worry about. Very few cysts are cancerous, but it needs to be biopsied. I can remove it if you want.” I did.

It is important to mention here that my husband is, for better or worse, a totally curious and competitive Guinness World Records kind of guy. Mostly, I love this about him. (Did I say mostly?)

Which was probably why, when Mark brought his black doctor’s bag over to our apartment, Bob did not absent himself. A little home surgery? My husband had nothing like this on his list of life experiences. I watched his excitement grow as Mark took a syringe and scalpel out of the bag and began to sterilize the area.

Always queasy about needles, I lay back on the floor, determined not to watch as Mark administered the shot of local anesthesia. Both men leaned in for a closer look.

“Can I do it?” Bob blurted out eagerly. “Will you let me use the scalpel?” They both stared at me; apparently this was my decision. How could I say no to my husband and yes to my first love?

True, my husband’s sudden desire to cut into me was sort of creepy. True, I was lying there like a calf waiting to be branded. At this surreal moment, however, what ran through my head was that of the holy trinity of important men in my life, the only one not in that room was my father.

With guidance from Mark, and some self-congratulatory comments about his steady hand, Bob deftly cut out the cyst. “Can I stitch her up?” he asked gleefully. I’d never seen my husband sew anything; now he wanted to start with my leg. But there was something more going on here, an intricate encounter between two men who were mutually respectful, but each with a different claim to my body. I closed my eyes.

The operation was a success, and the cyst was indeed benign. Two decades later, Mark is an accomplished surgeon with a winner of a wife and three beautiful girls. He remains our go-to phone call for medical advice.

Meanwhile, on my upper thigh, whether it’s just the way I heal or the clumsy work of an amateur surgeon, a small, lumpy scar remains. It’s a sweet reminder of that impulsive moment, almost 25 years ago, when I understood the unspoken importance of my husband’s desire to stamp me with a symbolic “She’s mine.”

LEE WOODRUFF is a CBS This Morning contributor and a best-selling author. Her latest book is the novel Those We Love Most.